Fueling environments typically store fuel in large storage tanks located beneath the ground, sometimes referred to as “underground storage tanks” (UST). To comply with environmental laws, rules, and regulations, these storage tanks may be double-walled and equipped with various leak detection sensors and inventory reconciliation systems. One popular leak detection sensor is sold by Veeder-Root Company of 125 Powder Forest Drive, Simsbury, Conn. 06070, the assignee of the present application, under the name “The MAG Plus Inventory Measurement Probe” (Mag Probe). This probe is typically matched with a tank monitor, such as the TLS-350R, also sold by Veeder-Root Company. Such probes measure a height of fuel within the storage tank and may optionally measure a height of water (if present). The measurements are reported to the tank monitor for usage by the operator of the fueling environment to evaluate and reconcile fuel inventory and/or detect leaks, as is well understood.
While the United States has many rules and regulations relating to leak monitoring within fueling environments, other locales have additional requirements for fueling environments. For example, countries such as India and Russia have seen a rise in fraud at fueling environments, and have consequently taken steps to combat such fraud. Specifically, these countries have become aware that dilution of the fuel within storage tanks may be used as a technique to defraud a customer. One way in which the diluted fuel is created is through the addition of alcohol to the fuel storage tank. The alcohol allows the water at the bottom of the fueling tank to mix with the fuel, and the diluted mixture is then dispensed as normal through the fuel dispensers.
To combat this fraud, some governments have mandated that fuel density be measured. If the density is outside of a predetermined allowable range, it may be inferred that the fuel has been adulterated. Even if some countries or governments do not have such legislation requiring measurement of density of fuel, some fuel distribution companies that operate service stations may nonetheless find it desirable to monitor the density of their fuel for quality control purposes.
Density measurements also assist in calculation of the mass of fluid within a storage container. Differences in mass may be used to perform leak detection for fluids in situations where normal volume detection techniques are inadequate (e.g., waste oil storage containers). These situations create additional demand for density measuring devices.
All the devices currently known to be available commercially that are capable of measuring fuel density in a conventional fueling environment fuel storage tank are stand alone peripherals, requiring their own power and interface connections. Furthermore, these devices tend to have a limited range of values over which fuel density can be measured. Such stand alone peripherals are not desirable as a result of these deficiencies.
An additional concern that arises in the measurement of fuel density is that the density of the fuel is not typically uniform at all fuel levels in an underground storage tank. For example, there may be thermal stratification which results in non-uniform densities at particular levels within the fuel storage tank. Likewise, surface thermal effects can be large. That is, when the surface of the fuel is much warmer than the bulk of the stored fuel, the density of the surface fuel relative to the bulk of the fuel is reduced. If the density of the fuel is measured just at the surface, the measurement will not accurately reflect the density of the bulk of the fuel. Any density measuring device should be able to address these issues.
In response to these concerns, the Assignee of the present invention presented the fuel density measurement system of commonly-owned U.S. patent application Ser. No. 11/048,145, filed Feb. 1, 2005. While the '145 Application provides one solution to the concerns raised above, there remains a need for a simpler solution.